1. Field of the Invention
The present invention relates generally to semiconductor devices sealed with resin, and more particularly, to a resin-sealed semiconductor device improved so as to prevent corrosion of the copper wire connecting the semiconductor element and the lead.
2. Description of the Background Art
FIG. 1 is a sectional view of a resin-sealed semiconductor device. A semiconductor element 4 is fixed onto dipad 5 by cement 6 such as of solder or resin. An aluminum electrode pad 41 is provided at a portion of semiconductor element 4. Lead 8 is disposed in the vicinity of semiconductor element 4. Lead 8 and aluminum electrode pad 41 are electrically connected by copper wire 7. Dipad 5, semiconductor element 4, copper wire 7, and one portion of lead 8 are sealed by an epoxy resin composition 9.
A conventional resin-sealed semiconductor device with the aforementioned structure has the following problems. A gap is generated between epoxy resin composition 9 for sealing and lead 8. A gap is also generated at the interface between epoxy resin composition 9 and semiconductor element 4. Through this gap, external moisture enters to corrode aluminum electrode pad 41 on semiconductor element 4 and copper wire 7. This corrosion causes deficiencies such as disconnection of copper wire 7.
The cause of this corrosion is said to result from the interaction of the above mentioned moisture and ionic impurities included in the resin, and the presence of organic acid included in the resin.
In a conventional resin-sealed type semiconductor device, epoxy resin composition superior in heat resistance and moisture resistance is used as the sealing agent. Chloride ions mixed in at the time of manufacturing, or bromine derived from the brominated epoxy resin used as a flame retarder is included in the epoxy resin. This halogen interacts with the moisture entering the sealing resin while diffusing to corrode the aluminum wire of the semiconductor device.
The organic acid in the sealing resin such as formic acid and acetic acid are known to corrode the aluminum wire.
Various methods have been proposed to suppress the above mentioned corrosion of aluminum wires.
Japanese Patent Laying-Open No. 60-38847 discloses a resin-sealed type semiconductor device in which the concentration of organic acid ion such as formic acid and acetic acid is less than 20 ppm. This is a proposal to prevent corrosion of aluminum wire by decreasing the organic acid ions in the resin.
Japanese Patent Laying-Open No. 60-80259 discloses a semiconductor device sealed with a resin composition including polyfunctional epoxy compound and molybdate.
Japanese Patent Laying-Open No. 60-84322 discloses a resin composition including polyfunctional epoxy compound and biphenyl tetracarboxylic acid anhydride for sealing semiconductors.
Japanese Patent Laying-Open No. 62-150860 discloses a semiconductor device having the semiconductor element and lead wires coated by a material including a certain organic phosphate or amine type compounds.
Japanese Patent Laying-Open No. 62-207319 discloses flame retarding epoxy resin composition including bismuth type inorganic ion-exchanger and brominated epoxy resin for sealing the semiconductor device.
Japanese Patent Laying-Open No. 62-285912 discloses a resin composition including ion catcher which captures halogen ions, alkali metal ions, and organic acid ions for sealing the semiconductor.
Japanese Patent Laying-Open No. 63-17925 discloses an epoxy resin composition including silver salt of organic acid and/or lead salt of organic acid for sealing the semiconductor.
Japanese Patent Laying-Open No. 61-19625 discloses an epoxy resin composition adding hydrotalcite type compound for sealing the semiconductor.
Japanese Patent Laying-Open No. 60-190453 discloses a resin composition including ferric acid, zirconic acid, titanic acid, and hydrated bismuth trioxide acid for sealing the semiconductor.
All the above mentioned prior art achieves the suppression of aluminum wire corrosion in relatively low temperature, and suppression regarding the occurrence of aluminum wire corrosion in an environment of high temperature is not mentioned anywhere.
Because a semiconductor device generates heat when used, the temperature of the entire device rises. This rise in temperature has a great effect on the reliability of the semiconductor device. Because gold wire was used as the lead in conventional semiconductor devices, there was no corrosion in the gold wire and at the junction of the gold wire and the aluminum electrode pad even in an environment of high temperature. Hence, there was no inconvenience. However, when more economical copper wire is used instead of gold wire, the problem of corrosion in the copper wire occurs at high temperatures (170.degree.-220.degree. C.).